US20060209538A1

US20060209538A1 - Backlight modules

Info

Publication number: US20060209538A1
Application number: US11/379,584
Authority: US
Inventors: Chih-Li Chang; Hung-Chen Kao
Original assignee: Hannstar Display Corp
Current assignee: Hannstar Display Corp
Priority date: 2004-11-17
Filing date: 2006-04-21
Publication date: 2006-09-21

Abstract

Backlight modules are provided. The backlight module includes a printed circuit board, a plurality of red light emitting diodes, a plurality of blue light emitting diodes, a plurality of green light emitting diodes and a plurality of white light emitting diodes. The plurality of red, blue, green and white light emitting diodes are disposed on the printed circuit board, defining a light emitting area. The plurality of white light emitting diodes is disposed at the periphery of the light emitting area. Wherein both the blue light emitting diodes include a blue light chip and the red light emitting diodes include a red light chip respectively, the green light emitting diodes include a larger green light chip or two equal sized green light chips to the blue and red light chips.

Description

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent application Ser. No. 10/990,878, filed on Nov. 17, 2004 and entitled “Backlight Modules”.

BACKGROUND

The invention relates to backlight modules and more particularly, to backlight modules utilizing light emitting diodes as light sources.
A conventional backlight module typically utilizes a cold cathode fluorescent lamp as a light source. Cold cathode fluorescent lamps, however, contain environmentally hazardous mercury.
Other conventional backlight modules utilize light emitting diodes (LEDs) as a light source, as shown in FIG. 1A. The backlight module includes a light source 12, a reflector 13, a diffuser 14 and a reflecting frame 15. The light source 12 comprises red, blue and green LEDs encircling the reflector 13. The lights emitted by red, blue and green LEDs are blended to white light, reflected and diffused by the reflector 13, diffuser 14 and reflecting frame 15 to form a planar light emitting surface. Some problems, however, occur at the corner and periphery of the conventional backlight module. Referring to FIG. 1B which shows a corner of the conventional backlight module of FIG. 1A, no LED is disposed at a first position I, a red LED is disposed at a second position II, a green LED is disposed at a third position III, and a blue LED is disposed at a fourth position IV. A red and a blue LED are disposed adjacent to the green LED which is disposed at the third position III, such that the blended light around the third position III is uniform. The red LED, which is disposed at the second position II, however, stands alone as no LED is placed at the first position I. Thus, the blended light near the first and second positions I and II is non-uniform. In other words, a chromatic aberration occurs at the corner and periphery of a conventional backlight module. One method of solving the problem is to cover these portions. This, however, reduces the overall display area.
Another small size backlight module utilizes white LEDs as a light source. The white light emitted by the white LED, however, is not as adequate as the white light blended from the red, blue and green LEDs. Thus, white LEDs are not utilized in large size backlight modules.
Increasing the luminance of the conventional backlight module is a key issue for display performance, however, luminance increase is limited by LED layout space and cost control.

SUMMARY

Backlight modules are provided. An exemplary embodiment of a backlight module comprises a printed circuit board, a red light emitting diode, a blue light emitting diodes a green light emitting diode and a white light emitting diode. The red, blues green and white light emitting diodes (LEDs) are disposed on the printed circuit board. The green light emitting diodes include a green light chip respectively, the red light emitting diodes include a red light chip respectively, and the blue light emitting diodes include a blue light chip respectively. Wherein the size of the green light chip is larger than the red and blue light chips.
In another embodiment of a backlight module, the green light emitting diodes respectively include two green light chips, the red light emitting diodes include a red light chip respectively, and the blue light emitting diodes include a blue light chip respectively. Wherein the size of the green light chip is equal to the red and blue light chips.
Some embodiments of a backlight module comprise a printed circuit board, a plurality of red LEDs, a plurality of blue LEDs, a plurality of green LEDs and a plurality of white LEDs. The plurality of red, blue, green and white LEDs are disposed on the printed circuit board, defining a light emitting area, the plurality of white LEDs is disposed at the periphery of the light emitting area.

DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a conventional backlight module;
FIG. 1B is a partial enlarged view of the backlight module according to FIG. 1A;
FIG. 2 is a schematic diagram illustrating a backlight module according to an embodiment of the invention;
FIG. 3A is a partial enlarged view illustrating a backlight module according to an embodiment of the invention;
FIG. 3B is a schematic diagram illustrating a backlight module according to an embodiment of the invention;
FIG. 4A is a partial enlarged view illustrating a backlight module according to an embodiment of the invention;
FIG. 4B is a schematic diagram illustrating a backlight module according to an embodiment of the invention;
FIG. 5A is a partial enlarged view illustrating a backlight module according to an embodiment of the invention;
FIG. 5B is a schematic diagram illustrating a backlight module according to an embodiment of the invention;
FIG. 6A is a schematic diagram illustrating a backlight module according to an embodiment of the invention;
FIG. 6B is a schematic diagram illustrating a backlight module according to an embodiment of the invention;
FIG. 7 is a schematic diagram illustrating a backlight module according to an embodiment of the invention;
FIG. 8 is a schematic diagram illustrating a backlight module according to an embodiment of the invention; and
FIG. 9 is a schematic diagram illustrating a backlight module according to an embodiment of the invention.

DETAILED DESCRIPTION

Backlight modules are provided. An exemplary embodiment of a backlight module comprises a printed circuit board 21, a light source 22 and a reflector 23, as shown in FIG. 2. The light source 22 comprises a red light emitting diode (LED) R, a blue LED B, a green LED G and a white LED W. The red, blue, green and white LEDs R, B, G and W are disposed on the printed circuit board 21 which is disposed on the reflector 23. The reflector 23 reflects light emitted by the red, blue, green and white LEDs R, B, G and W in conjunction with a diffuser (not shown) to form a planar light emitting surface.
FIG. 3A is a partial enlarged view and FIG. 3B is a schematic diagram of an embodiment of a backlight module. In FIGS. 3A and 3B, the backlight module is an edge type backlight module, comprising a printed circuit board 21, a light source and a reflector 23. The light source is constructed by red LEDs R, blue LEDs B, green LEDs G and white LEDs W.
Referring to FIG. 3B, the red, blue, green and white LEDs R, B, G and W are disposed along a line and at two opposite edges of the printed circuit board 21, defining a rectangular light emitting area A. The white LEDs W are disposed at corners of the light emitting area A. At one mentioned line on the edge of the printed circuit board 21 (the other line is the same), the white LEDs W are disposed at both ends of the line. Referring back to FIG. 3A, the white LEDs W are disposed at corners or the periphery of the backlight module to solve the chromatic aberration problem of the conventional backlight module.
In some embodiments, the number of red, blue and green LEDs R, B and G may be the same. When the number differs, causing chromatic aberrations, white LEDs are employed to increase chromatic uniformity. Moreover, the collocation of the LEDs is not limited to the arrangement depicted in FIG. 3B.
FIG. 4A is a partial enlarged view and FIG. 4B is a schematic diagram of an embodiment of a backlight module. In FIGS. 4A and 4B, the backlight module is an edge type backlight module. Descriptions of elements using the same reference numbers are omitted.
The red, blue, green and white LEDs R, B, G and W are disposed at the periphery of the printed circuit board 21, for example, respectively aligned on four edges of the printed circuit board 21, defining a rectangular light emitting area A. The white LEDs W are disposed at the corners of the light emitting area A. In other words, when viewing only one edge of the printed circuit board 21, which is identical to the other edges, the white LEDs W are disposed at each end of each edge.
FIGS. 5A and 5B are schematic diagrams of an embodiment of a backlight module. In FIGS. 5A and 5B, the backlight module is a direct type backlight module, comprising a printed circuit board 21 and a light source. The light source comprises red LEDs (LEDs) R, blue LEDs B, green LEDs G and white LEDs W.
The red, blue, green and white LEDs R, B, G and W are disposed on the printed circuit board 21, along three lines (the number of lines is not limited), defining a rectangular light emitting area A. The white LEDs W are disposed at the corners or periphery of the light emitting area A. In other words, when viewing only one mentioned line on the printed circuit board 21, which is identical to the other two lines, the white LEDs W are disposed at each end of each line.
In some embodiments, in the light emitting area A, the red, blue, and green LEDs R, B and G are alternately arranged. Namely, the two adjacent LEDs have different colors, such that the blended light can be more uniform. The columns and rows of the LEDs may vary according to requirements.
In some embodiments, the number of red, blue and green LEDs R, B and G may be the same. When the number differs, causing chromatic aberrations, white LEDs are employed to increase chromatic uniformity. Moreover, the collocation of the LEDs is not limited the arrangement depicted in figure.
FIGS. 6A and 6B are schematic diagrams of an embodiment of a backlight module. In FIGS. 6A and 6B, the backlight module is a direct type backlight module. Descriptions of elements using the same reference numbers are omitted.
The red, blue, green and white LEDs R, B, G and W are disposed on the printed circuit board 21 to form a rectangular pattern, defining a rectangular light emitting area A. The white LEDs W are disposed at the corners of the light emitting area A. In other words, when viewing only one side of the rectangular pattern, which is identical to the other sides, the white LEDs W are disposed at each end of each side.
Referring to FIG. 6B, when the backlight module is large, except for the mentioned LEDs, rows of the LEDs may be employed in the light emitting area A, to increase overall brightness.
In some embodiments, in the light emitting area A, the red, blue, and green LEDs R, B and G are alternately arranged. Namely, the two adjacent LEDs have different colors, such that the blended light can be more uniform.
FIG. 7 is a schematic diagram of an embodiment of a backlight module. In FIG. 7, the backlight module is a direct type backlight module. Descriptions of elements using the same reference numbers are omitted.
The red, blue, green and white LEDs R, B, G and W are disposed on the printed circuit board 21 and arranged in a zigzag pattern, defining a light emitting area A. The white LEDs are disposed at the periphery of the light emitting area A. In other words, the white LEDs W are disposed at the points of the zigzag pattern.
FIG. 8 is a schematic diagram of an embodiment of a backlight module. In FIG. 8, the backlight module is a direct type backlight module. Descriptions of elements using the same reference numbers are omitted.
The red, blue, green and white LEDs R, B, G and W are disposed on the printed circuit board 21 and arranged in a square-wave pattern, defining a light emitting area A. The white LEDs are disposed at the periphery of the light emitting area A. In other words, the white LEDs W are disposed at the outer extremities of the square-wave pattern.
FIG. 9 is a schematic diagram of an embodiment of a backlight module. In FIG. 9, the backlight module is a direct type backlight module. Descriptions of elements using the same reference numbers are omitted.
The red, blue, green and white LEDs R, B, G and W are disposed on the printed circuit board 21 and arranged in a wave shape, defining a light emitting area A. The white LEDs are disposed at the periphery of the light emitting area A. In other words, the white LEDs W are disposed at the crests and the troughs of the wave shape.
The green light emitting diodes include a green light chip respectively, the red light emitting diodes include a red light chip respectively, and the blue light emitting diodes include a blue light chip respectively. Wherein the size of the green light chip is larger than the red and blue light chips.
In another backlight module embodiment, the green light emitting diodes include two green light chips respectively, the red light emitting diodes include a red light chip respectively and the blue light emitting diodes include a blue light chip respectively. Wherein the size of the green light chip is equal to the red and blue light chips.

Referring to table 1, wherein column type I shows the package types of red, green, and blue light emitting diodes used in the conventional backlight modules, wherein the sizes of the light chips are represented as mil (length unit, 0.001 inch) and the center luminance of the backlight module is represented as nits (luminance unit). Column Type II shows the package type in an embodiment of the invention, wherein the green light emitting diodes respectively include two green light chips, the red light emitting diodes include a red light chip respectively, and the blue light emitting diodes include a blue light chip respectively. The center luminance of type II shows a 58% increase over type I. Column type III shows the package type in another embodiment of the invention, wherein the green light emitting diodes include a green light chip respectively, the red light emitting diodes include a red light chip respectively, and blue light emitting diodes include a red light chip respectively. Wherein the green light chip is larger than the red and the blue light chips. The center luminance of type III shows a 56% increase over type I. To result in a center luminance increase, type II and type III merely change the numbers or the sizes of the green light chips which slightly influence the final size of green light emitting diodes and printed circuit board layout.

TABLE 1


Type I	Type II	Type III

Light Emitting	Red: 14 mil	Red: 14 mil	Red: 14 mil
Diode	Green: 14 mil	Green: 14 mil × 2	Green: 24 mil
Package Type	Blue: 14 mil	Blue: 14 mil	Blue: 14 mil
Center	158	250	247
Luminance(nits)
Center Luminance	100%	158%	156%
Variation

While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

Claims

1. A backlight module, comprising:

a printed circuit board;

a plurality of red light emitting diodes, including a red light chip respectively;

a plurality of blue light emitting diodes, including a blue light chip respectively;

a plurality of green light emitting diodes, including a green light chip respectively; and

a plurality of white light emitting diodes,

wherein the plurality of red, blue, green and white light emitting diodes are disposed on the printed circuit board, defining a light emitting area, and the size of the green light chip is larger than the red light chip and the blue light chip.

2. The backlight module as claimed in claim 1, further comprising a reflector adjoined to the printed circuit board, reflecting the light from the plurality of red, blue, green and white light emitting diodes to form a planar light emitting surface.

3. The backlight module as claimed in claim 1, wherein the light emitting area is rectangular.

4. The backlight module as claimed in claim 3, wherein the plurality of white light emitting diodes is disposed at the corners of the light emitting area.

5. The backlight module as claimed in claim 1, wherein the red, blue and green light emitting diodes are alternately arranged.

6. The backlight module as claimed in claim 1, wherein the plurality of red, blue, green and white light emitting diodes are arranged in a zigzag pattern with the white light emitting diodes disposed at the points thereof.

7. The backlight module as claimed in claim 1, wherein the plurality of red, blue, green and white light emitting diodes are arranged in a square-wave pattern with the white light emitting diodes disposed at the outer extremities thereof.

8. The backlight module as claimed in claim 1, wherein the plurality of red, blue, green and white light emitting diodes are arranged in a wave shape with the white light emitting diodes disposed at the crests and the troughs thereof.

9. A backlight module, comprising:

a printed circuit board;

a red light emitting diode, including a red light chip;

a blue light emitting diode, including a blue light chip;

a green light emitting diode, including a green light chip; and

a white light emitting diode,

wherein the red, blue, green and white light emitting diodes are disposed on the printed circuit board, and the size of the green light chip is larger than the red light chip and the blue light chip.

10. The backlight module as claimed in claim 9, further comprising a reflector adjoined to the printed circuit board, reflecting the light from the red, blue, green and white light emitting diodes to form a planar light emitting surface.

11. The backlight module as claimed in claim 9, wherein the red, blue, green and white light emitting diodes are disposed along a line, the white light emitting diode is disposed at an end of the line.

12. The backlight module as claimed in claim 9, wherein the white light emitting diode is disposed at an edge of the printed circuit board.

13. The backlight module as claimed in claim 9, wherein the red, blue and green light emitting diodes are alternately arranged.

14. The backlight module as claimed in claim 9, further comprising a plurality of the red, blue, green and white light emitting diodes.

15. The backlight module as claimed in claim 14, wherein the numbers of the red, blue and green light emitting diodes are equal.

16. The backlight module as claimed in claim 14, wherein the plurality of red, blue, green and white light emitting diodes are disposed along a line and the red, blue and green light emitting diodes are alternately arranged.

17. The backlight module as claimed in claim 14, wherein the plurality of red, blue, green and white light emitting diodes are arranged in a zigzag pattern with the white light emitting diodes disposed at the points thereof.

18. The backlight module as claimed in claim 14, wherein the plurality of red, blue, green and white light emitting diodes are arranged in a square-wave pattern with the white light emitting diodes disposed at the outer extremities thereof.

19. The backlight module as claimed in claim 14, wherein the plurality of red, blue, green and white light emitting diodes are arranged in a wave shape with the white light emitting diodes disposed at the crests and the troughs thereof.

20. The backlight module as claimed in claim 14, wherein the plurality of white light emitting diodes is disposed at the periphery of the printed circuit board.

21. A backlight module, comprising:

a printed circuit board;

a red light emitting diode, including a red light chip;

a blue light emitting diode, including a blue light chip;

a green light emitting diode, including two green light chip; and

a white light emitting diode,

wherein the red, blue, green and white light emitting diodes are disposed on the printed circuit board, and the sizes of the red, green and blue light chips are equal.